.wrapper>div {
    position: fixed;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: auto;
    background: skyblue;
    width: 60px;
    height: 60px;
    border-radius: 50%;
    /* 关键帧动画 */
    /* animation-name 动画脚本 
    animation-duration 持续时间
    animation-iteration-count 执行次数
    anmation-timing-function 运动速率 */
    animation: loading 1.4s infinite ease-in;
}
.wrapper>div:nth-child(2) {
    animation-delay: -0.7s;
}
@keyframes loading {
    0%,100% {
        transform: scale(0);
    }
    50% {
        transform: scale(1);
    }
}